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Fri, 17 Apr 2026 15:08:43 +0000 (UTC) Received: from fweimer-oldenburg.csb.redhat.com (unknown [10.44.32.186]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 92AE030001BE; Fri, 17 Apr 2026 15:08:35 +0000 (UTC) From: Florian Weimer To: =?utf-8?Q?Andr=C3=A9?= Almeida Cc: Catalin Marinas , Will Deacon , Thomas Gleixner , Mark Rutland , Mathieu Desnoyers , Sebastian Andrzej Siewior , Carlos O'Donell , Peter Zijlstra , Rich Felker , Torvald Riegel , Darren Hart , Ingo Molnar , Davidlohr Bueso , Arnd Bergmann , "Liam R . Howlett" , Uros Bizjak , Thomas =?utf-8?Q?Wei=C3=9Fschuh?= , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-dev@igalia.com Subject: Re: [PATCH RFC 1/2] arm64: vdso: Prepare for robust futex unlock support In-Reply-To: <20260417-tonyk-robust_arm-v1-1-03aa64e2ff1a@igalia.com> (=?utf-8?Q?=22Andr=C3=A9?= Almeida"'s message of "Fri, 17 Apr 2026 11:56:10 -0300") References: <20260417-tonyk-robust_arm-v1-0-03aa64e2ff1a@igalia.com> <20260417-tonyk-robust_arm-v1-1-03aa64e2ff1a@igalia.com> Date: Fri, 17 Apr 2026 17:08:32 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-MFC-PROC-ID: KW-m-TS0BDNb-zCM1HYnnDxiiLMXNdzDewftqGIO4Fs_1776438525 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260417_160900_564918_6AAFC45B X-CRM114-Status: GOOD ( 14.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org * Andr=C3=A9 Almeida: > There will be a VDSO function to unlock non-contended robust futexes in > user space. The unlock sequence is racy vs. clearing the list_pending_op > pointer in the task's robust list head. To plug this race the kernel need= s > to know the critical section window so it can clear the pointer when the > task is interrupted within that race window. The window is determined by > labels in the inline assembly. > > Signed-off-by: Andr=C3=A9 Almeida > --- > RFC: Those symbols can't be found by the linker after patch 2/2, it fails= with: > > ld: arch/arm64/kernel/vdso.o: in function `vdso_futex_robust_unlock_updat= e_ips': > arch/arm64/kernel/vdso.c:72:(.text+0x200): undefined reference to `__fute= x_list64_try_unlock_cs_success' > ld: arch/arm64/kernel/vdso.o: relocation R_AARCH64_ADR_PREL_PG_HI21 again= st symbol `__futex_list64_try_unlock_cs_success' which may bind externally = can not be used when making a shared object; recompile with -fPIC > arch/arm64/kernel/vdso.c:72:(.text+0x200): dangerous relocation: unsuppor= ted relocation I think your GLOBLS definition adds a 64 suffix. That shouldn't be necessary on AArch64. It's not reflected in the references, so you end up with an undefined symbol error. Thanks, Florian